Cepheus, the King

Cepheus is a northern constellation, one of Ptolemy's forty-eight, representing the mythical king of Aethiopia, husband of Cassiopeia and father of Andromeda, and so one of the royal figures of the great Perseus myth set together in the sky. Its five main stars form a shape like a child's drawing of a house, near the pole. It is astronomically important for its variable star Delta Cephei, the prototype of the Cepheid variables, whose regular pulsations gave astronomers a means of measuring cosmic distances. In astronomical tradition the constellation is a pattern of stars rather than a zodiac sign. These are the features of Cepheus as the classical and modern traditions describe it, distinct from any astrological reading; the king stands beside his queen Cassiopeia in the circumpolar sky, both set among the stars in the aftermath of their story.

Cepheus borders Camelopardalis, the early seventeenth-century giraffe introduced to cover the large, faint stretch of circumpolar sky between the king, the two Bears and Cassiopeia that Ptolemy's original forty-eight had left entirely unmarked. Delta Cephei's discovery as a regular pulsating variable, and the subsequent identification of the period-luminosity relation by Henrietta Swan Leavitt in the early twentieth century, made Cepheid variables the essential first rung of the cosmic distance ladder, the method by which astronomers first measured distances to other galaxies.